The present invention relates to data storage systems, and more particularly, to hybrid storage systems having tiers of data storage.
In magnetic storage systems, data are read from, and written onto, a magnetic recording medium utilizing magnetic transducers. Data are written on the magnetic recording medium by moving a magnetic recording transducer to a position over the medium where the data are to be stored. The magnetic recording transducer then generates a magnetic field, which encodes the data into the magnetic medium. Data are read from the medium by similarly positioning the magnetic read transducer and then sensing the magnetic field of the magnetic medium. Read and write operations may be independently synchronized with the movement of the medium to ensure that the data can be read from, and written to, the desired location on the medium.
In a tape drive system, magnetic tape is moved over the surface of the tape head at high speed. Usually the tape head is designed to minimize the spacing between the head and the tape. The spacing between the magnetic head and the magnetic tape is crucial so that the recording gaps of the transducers, which are the source of the magnetic recording flux, are in near contact with the tape to effect writing sharp transitions. Also when the read element is in near contact with the tape, effective coupling of the magnetic field from the tape to the read element is possible.
In the near future, with the adoption of improved media, the cost of storing information (on a per byte basis) on tape is expected to decline by a factor of five or more with respect to magnetic disk. Also, short-term and long-term reliability will continue to favor tape-based storage. Furthermore, as more mass storage is allocated to cloud networks, most storage will be in large libraries, rather than on individual drives, which is a consideration favoring tape-based storage. One historical disadvantage of tape-based storage with respect to disk-based storage was the relatively poor access time associated with tape-based storage, with the time required to bring the tape to the tape drive and then spool the tape to the file location typically averaging about 40 seconds.